1. Technical Field
The present invention relates in general to hard disk drives and, in particular, to an improved system, method, and apparatus for a hard disk drive having a recirculation filter with shrouding that shrouds the rims of disks at the inlet and outlet of the filter.
2. Description of the Related Art
Data access and storage systems typically comprise one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. One to six disks are usually stacked on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute.
A typical HDD also utilizes an actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The surface of the slider facing the disk is aerodynamically shaped to create an air bearing in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
Typically, a slider is formed with an aerodynamic pattern of protrusions on its air bearing surface that enables the slider to fly at a substantially constant height close to the disk during operation of the disk drive. A slider is associated with each side of each disk and flies just over the disk's surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops a torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
Some disk drive designs use an air recirculation filter to reduce contamination inside the disk drive. Since the amount of available space inside a disk drive enclosure is typically very limited, it can be difficult to accommodate such a filter. One difficulty in determining the proper location for a recirculation filter is selecting a space that is suitable for both good clean up efficiency and one that will have a minimum impact on other important criteria, specifically track misregistration (TMR) and aerodynamic power consumption.
In small form factor drives, the lack of space usually results in placing the recirculation filter 11 at the so-called “11 o'clock” location. FIGS. 1-3 depict one type of prior art placement of a filter at the 11 o'clock position with unshrouded inlet 13 and outlet 15. As best shown in FIG. 2, the rim 17 of the disk 19 is completely exposed at both the inlet 13 and at the outlet 15 in front of the air filter 11. As shown in FIG. 3, the filter inlet 13 and outlet 15 are open all the way to the casting floor 21.
Wherever the disk is not shrouded the airflow separates from the disk in a highly turbulent and unsteady manner. The result is undesirable unsteady forces on the disk which contribute to position errors (as indicated by the position error signal (PES)) of the read/write head. With such physical interruptions adjacent to the disks, disk flutter is exacerbated due to an increase in flow turbulence in between and around the filter.
The unsteadiness of the aerodynamic forces has frequency components that are beyond the bandwidth of current servo systems. Such forces cannot be corrected or, worst yet, are even amplified by the servo system. In principle, the high frequency components could be counteracted with systems based on micro-actuators and the like, but such systems can be quite expensive and prone to their own increased aerodynamic excitation. Thus, an improved solution for overcoming the limitations and problems associated with the prior art would be desirable.